Prewetting of substrate before immersion exposure

ABSTRACT

A lithographic projection apparatus includes a support structure configured to hold a patterning device. The patterning device is configured to pattern a beam of radiation according to a desired pattern. The lithographic apparatus further includes a substrate table configured to hold a substrate. The substrate has a surface coated at least partially with a layer of radiation sensitive material. The lithographic apparatus also includes a projection system configured to project the patterned beam onto a target portion of the substrate, and a liquid supply system. The liquid supply system is configured to supply a prewetting liquid on top of the layer of radiation sensitive material to prewet the substrate, and is configured to supply an immersion liquid in a space between the prewet substrate and at least a portion of the projection system.

This application is a divisional of U.S. patent application Ser. No.11/005,219, filed Dec. 7, 2004, now U.S. Pat. No. 7,196,770 the entirecontents of which is herein incorporated by reference.

FIELD

The present invention relates to a lithographic apparatus and inparticular to an immersion lithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid (referred to as an “immersion liquid”)having a relatively high refractive index, e.g. water, so as to fill aspace between the final element of the projection system and thesubstrate. The point of this is to enable imaging of smaller featuressince the exposure radiation will have a shorter wavelength in theliquid. (The effect of the liquid may also be regarded as increasing theeffective numerical aperture (NA) of the system and also increasing thedepth of focus.) Other immersion liquids have been proposed, includingwater with solid particles (e.g. quartz) suspended therein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see for example United States patent U.S. Pat. No.4,509,852, hereby incorporated in its entirety by reference) means thatthere is a large body of liquid that must be accelerated during ascanning exposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

One of the solutions proposed is for a liquid supply system to provideliquid (also referred to as an “immersion liquid”) on only a localizedarea of the substrate and in between the final element of the projectionsystem and the substrate (the substrate generally has a larger surfacearea than the final element of the projection system). One way which hasbeen proposed to arrange for this is disclosed in PCT patent applicationno. WO 99/49504, hereby incorporated in its entirety by reference. Asillustrated in FIGS. 2 and 3, liquid is supplied by at least one inletIN onto the substrate, preferably along the direction of movement of thesubstrate relative to the final element, and is removed by at least oneoutlet OUT after having passed under the projection system. That is, asthe substrate is scanned beneath the element in a −X direction, liquidis supplied at the +X side of the element and taken up at the −X side.FIG. 2 shows the arrangement schematically in which liquid is suppliedvia inlet IN and is taken up on the other side of the element by outletOUT which is connected to a low pressure source. In the illustration ofFIG. 2 the liquid is supplied along the direction of movement of thesubstrate relative to the final element, though this does not need to bethe case. Various orientations and numbers of in- and out-letspositioned around the final element are possible, one example isillustrated in FIG. 3 in which four sets of an inlet with an outlet oneither side are provided in a regular pattern around the final element.

SUMMARY

In conventional immersion lithography, the substrate coated with aradiation sensitive layer or resist layer is brought in contact with theimmersion liquid only when the substrate is exposed to radiation.

However, due to the “hydrophobic” nature of the resist, the substrateresist layer has a tendency to repel the immersion liquid at theinterface between the liquid and the resist layer on the substrate. As aresult, gas (e.g., air) may be trapped between the resist layer and theliquid interface. Furthermore, on a microscopic scale, the surface ofresist layer, albeit finished to be substantially flat, is not perfectlyflat and has a topography that increases the chance of having gastrapped inside crevices in the topography of the surface of the resistlayer. The gas trapped between the resist layer and the liquid interfacecan lead to formation of gas bubbles which can lead to printable defectson the resist layer as well as alter the characteristics of theradiation reaching the resist layer. The presence of gas bubbles or anyother impurity in the path of the radiation and in particular at thesurface of the resist layer, can seriously affect the imaging quality,for example, by being within the depth of focus.

According to an aspect of the present invention, there is provided Adevice manufacturing method, comprising applying, in a lithographicapparatus, a prewetting liquid on top of a layer of radiation sensitivematerial of a substrate, on a substrate table, or on both, providing animmersion liquid for use in projecting a patterned beam of radiation onthe prewet substrate and/or substrate table, and projecting a patternedbeam of radiation, through the immersion liquid, onto the substrateand/or the substrate table.

In an embodiment of the invention, the prewetting liquid hassubstantially a same chemical composition as the immersion liquid. Theprewetting liquid may comprise, for example, water or a topcoat. Theimmersion liquid may comprise water, for example.

In an embodiment of the invention, applying the prewetting liquidreduces bubbles of gas trapped between ridges in a surface of theradiation sensitive material. In an embodiment of the invention,applying the prewetting liquid on the substrate fills voids in a surfaceof the radiation sensitive material with the prewetting liquid. In anembodiment of the invention, substantially all chemicals, particles, orboth of the radiation sensitive material are leached into the prewettingliquid. In an embodiment of the invention, applying the prewettingliquid renders a surface of the radiation sensitive material compatiblewith the immersion liquid. In an embodiment of the invention, applyingthe prewetting liquid renders a surface of the radiation sensitivematerial less repellent to the immersion liquid. In an embodiment of theinvention, the prewetting liquid is at least partially transparent tothe patterned beam of radiation.

The method may further include removing prewetting liquid from theprewet substrate before providing the immersion liquid.

Another aspect of the present invention is to provide a lithographicprojection apparatus. The lithographic projection apparatus includes asupport structure configured to hold a patterning device. The patterningdevice is configured to pattern a beam of radiation according to adesired pattern. The lithographic projection apparatus. also includes asubstrate table configured to hold a substrate. The substrate has asurface coated at least partially with a layer of radiation sensitivematerial. The lithographic projection apparatus further includes aprojection system configured to project the patterned beam onto a targetportion of the substrate, and a liquid supply system. The liquid supplysystem is configured to supply a prewetting liquid on top of the layerof radiation sensitive material to prewet the substrate, and isconfigured to supply an immersion liquid in a space between the prewetsubstrate and at least a portion of the projection system.

In an embodiment of the invention, the prewetting liquid hassubstantially a same chemical composition as the immersion liquid. Theprewetting liquid may comprise, for example, water or a top coat. Theimmersion liquid may comprise, for example, water.

In an embodiment of the invention, the prewetting liquid is at leastpartially transparent to the patterned beam.

In an embodiment of the invention, the liquid supply system isconfigured to supply the prewetting liquid at a substantially samelocation in the apparatus as the immersion liquid. In an embodiment ofthe invention, the liquid supply system comprises a first liquid supplystructure configured to supply the prewetting liquid at a first locationin the apparatus and a second liquid supply structure configured tosupply the immersion liquid at a second location in the apparatus. Thefirst location can be a location of a measuring station in theapparatus. The second location can be allocation of an exposure stationin the apparatus.

In an embodiment of the present invention, the liquid supply systemincludes an inlet connected to a liquid reservoir adapted to supplyliquid to a surface of the substrate and an outlet connected to a pumpadapted to remove liquid from the surface of the substrate. The liquidsupply may also include an outlet configured to remove prewetting liquidfrom the prewet substrate before supply of immersion liquid to theprewet substrate.

A further aspect of the present invention is to provide a method ofpreparing a substrate provided at least partially with a layer ofradiation sensitive material, prior to applying an immersion liquid tothe substrate and exposing the substrate to a patterned beam ofradiation in an immersion lithographic apparatus. The method includescoating at least a portion of a surface of the layer of radiationsensitive material with a liquid chemical non-sensitive to the patternedbeam of radiation, the liquid chemical remaining in liquid form at leastuntil application of the immersion liquid in the apparatus in theimmersion lithographic apparatus.

In an embodiment of the invention, the liquid chemical is less repellentto the immersion liquid applied in the apparatus than the radiationsensitive material is to the immersion liquid. The liquid chemical mayhave substantially a same chemical composition as the immersion liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 depicts another liquid supply system in relation to a substrateand substrate table according to an embodiment of the present invention;

FIG. 7 is an enlargement of an area in FIG. 6;

FIG. 8A depicts a substrate coated with a resist with a prewet liquiddeposited on the resist;

FIG. 8B depicts a substrate coated with a resist with a prewet liquiddeposited on the resist and with an immersion liquid applied on theprewet resist;

FIG. 9A is side view of a lithographic apparatus with a prewettingliquid supply system according to an embodiment of the invention;

FIG. 9B is a top view of a lithographic apparatus with a prewettingliquid supply system according to an embodiment of the invention; and

FIG. 10 shows a diagram of the various steps taking place in alithographic apparatus during transfer of a substrate to and fromprewetting according to an embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam PB (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PLconfigured to project a pattern imparted to the radiation beam PB bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam PB passes through the projection system PL, which focusesthe beam onto a target portion C of the substrate W. An immersion hoodIH, which is described further below, supplies immersion liquid to aspace between the final element of the projection system PL and thesubstrate W.

With the aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam PB.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe mask MA with respect to the path of the radiation beam PB, e.g.after mechanical retrieval from a mask library, or during a scan. Ingeneral, movement of the mask table MT may be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the first positioner PM. Similarly,movement of the substrate table WT may be realized using a long-strokemodule and a short-stroke module, which form part of the secondpositioner PW. In the case of a stepper (as opposed to a scanner) themask table MT may be connected to a short-stroke actuator only, or maybe fixed. Mask MA and substrate W may be aligned using mask alignmentmarks M1, M2 and substrate alignment marks P1, P2. Although thesubstrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (theseare known as scribe-lane alignment marks).

Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

-   -   1. In step mode, the mask table MT and the substrate table WT        are kept essentially stationary, while an entire pattern        imparted to the radiation beam is projected onto a target        portion C at one time (i.e. a single static exposure). The        substrate table WT is then shifted in the X and/or Y direction        so that a different target portion C can be exposed. In step        mode, the maximum size of the exposure field limits the size of        the target portion C imaged in a single static exposure.    -   2. In scan mode, the mask table MT and the substrate table WT        are scanned synchronously while a pattern imparted to the        radiation beam is projected onto a target portion C (i.e. a        single dynamic exposure). The velocity and direction of the        substrate table WT relative to the mask table MT may be        determined by the (de-)magnification and image reversal        characteristics of the projection system PL. In scan mode, the        maximum size of the exposure field limits the width (in the        non-scanning direction) of the target portion in a single        dynamic exposure, whereas the length of the scanning motion        determines the height (in the scanning direction) of the target        portion.    -   3. In another mode, the mask table MT is kept essentially        stationary holding a programmable patterning device, and the        substrate table WT is moved or scanned while a pattern imparted        to the radiation beam is projected onto a target portion C. In        this mode, generally a pulsed radiation source is employed and        the programmable patterning device is updated as required after        each movement of the substrate table WT or in between successive        radiation pulses during a scan. This mode of operation can be        readily applied to maskless lithography that utilizes        programmable patterning device, such as a programmable mirror        array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a seal member which extends along at least a part of aboundary of the space between the final element of the projection systemand the substrate table. Such a solution is illustrated in FIG. 5. Theseal member is substantially stationary relative to the projectionsystem in the XY plane though there may be some relative movement in theZ direction (in the direction of the optical axis). A seal is formedbetween the seal member and the surface of the substrate.

Referring to FIG. 5, reservoir 10 forms a contactless seal to thesubstrate around the image field of the projection system so that liquidis confined to fill a space between the substrate surface and the finalelement of the projection system. The reservoir is formed by a sealmember 12 positioned below and surrounding the final element of theprojection system PL. Liquid is brought into the space below theprojection system and within the seal member 12. The seal member 12extends a little above the final element of the projection system andthe liquid level rises above the final element so that a buffer ofliquid is provided. The seal member 12 has an inner periphery that atthe upper end, in an embodiment, closely conforms to the shape of theprojection system or the final element thereof and may, e.g., be round.At the bottom, the inner periphery closely conforms to the shape of theimage field, e.g., rectangular though this need not be the case.

The immersion liquid is confined in the reservoir by a gas seal 16between the bottom of the seal member 12 and the surface of thesubstrate W. The gas seal is formed by gas, e.g. air or synthetic airbut, in an embodiment, N₂ or an inert gas, provided under pressure viainlet 15 to the gap between seal member 12 and substrate and extractedvia first outlet 14. The overpressure on the gas inlet 15, vacuum levelon the first outlet 14 and geometry of the gap are arranged so thatthere is a high-velocity gas flow inwards that confines the liquid. Sucha system is disclosed in U.S. patent application Ser. No. 10/705,783,hereby incorporated in its entirety by reference.

FIG. 6 is an enlargement of FIG. 5 around an exposure area of thesubstrate. FIG. 6 shows the substrate W ready for processing in alithographic apparatus of, for example, FIG. 1. A layer of radiationsensitive material RES (i.e. the so called “resist” or “photoresist”) iscoated on top of a surface of the substrate W. The radiation sensitivematerial RES is approximately 200 nm thick. The resist layer RES, albeitfinished to be substantially flat, is not perfectly flat and has asurface topography that has ridges 20.

Furthermore, as shown in FIG. 7 which is an enlargement of area A inFIG. 6, due to the “hydrophobic” nature of the material of the resistlayer RES, the resist layer RES has a tendency to repel the immersionliquid LIQ at the interface 22 between the immersion liquid LIQ and theresist layer RES on the substrate W. In other words, the surface 20 ofthe resist RES has tendency of not wetting easily or completely.Therefore, in order to properly wet the surface 20 of the resist RES atthe area of exposure, the immersion liquid may be kept for a certainlength of time in contact with the resist RES to allow the properwetting. However, this will require waiting a significant period of timefor proper wetting of the area of exposure each time a new targetportion C, i.e., dry portion, of the substrate W is positionedunderneath the exposure system for irradiation. This situation may notbe desirable as it will likely slow down the manufacturing process whichwill result in a loss in throughput.

Although the word “hydrophobic” meaning “repellent to water,” is used,it must be appreciated that the immersion liquid is not limited to waterbut can be any suitable liquid. Thus, the word “hydrophobic” should beinterpreted in this application in its broader sense to mean “repellentto liquid.”

In addition, due to the ridged topography of the surface of the resist,bubbles of gas 24 may be trapped inside crevasses between ridges in theresist layer RES and a surface of immersion liquid LIQ. The gas bubblestrapped at the interface 22 between the immersion liquid LIQ and theresist layer RES may lead to printable defects on the resist layer RESand/or cause scattering of radiation passing through the liquid and thusalter the characteristics of the radiation reaching the resist layerwhile scanning. This can seriously affect the image quality exposed onthe substrate. In addition, due to a ridged topography of a surface ofthe substrate table, bubbles of gas may also be trapped inside crevassesbetween ridges of the substrate table surface. The gas bubbles trappedin the surface of the substrate table, for example at an area where animage sensor is located on the surface of the substrate table, may alsolead to errors in measurements.

Further, the bubbles may eventually be released from their traps withtime or with motion of the liquid. Because in a localized liquid supplysystem a spot of liquid is moved from a target area of the substrate toanother target area of the substrate for each exposure, it may requiresome waiting time for the bubbles to be sufficiently released at eachnew target area of the substrate. However, waiting for a certain timeperiod at each exposure target area may render the scanning timeexcessively long. This is not desirable because manufacturing will beslowed and as a result throughput will suffer.

Another problem that may occur when the immersion liquid gets intocontact with a surface of the resist layer is that one or more chemicalsof the resist layer may leach into the liquid. The presence of achemical inside the liquid may alter the physical and opticalcharacteristic of the liquid, possibly leading to deterioration ofimaging during scanning. The presence of a chemical inside the liquidmay also lead to contamination of the projection system and thus todeterioration of imaging. A solution to this problem may be sufficientlyflushing the liquid at each target location. However, this may be a timeconsuming task and even if the liquid is flushed, the liquid may stillbe “tainted” by the presence of a small amount of a chemical of theresist layer that leached into the liquid.

In order to overcome one or more of the above and other deficiencies,the resist layer RES may be prewet using a prewetting liquid PLIQ prior,for example, to bringing the substrate W into contact with the immersionliquid LIQ. The prewetting liquid PLIQ may be allowed to contact theresist layer RES substantially in its entirety and the ridged topographyof the resist layer RES may thus be filled with the prewetting liquidPLIQ, as shown in FIG. 8. Furthermore, a surface of the substrate tablemay also be prewet using the prewetting liquid PLIQ. In this way, gasbubbles trapped in the surface of the substrate table, for example at anarea where an image sensor is located on the surface of the substratetable, may be allowed to escape prior to moving the substrate table tothe exposure station or taking a measurement in the measurement station.

As illustrated in FIG. 8A, which shows an enlargement of an area of thesubstrate, a prewetting liquid layer PLIQ is deposited on top of theresist layer RES, thus, filling substantially all the voids that maytrap gas. As a result, gas bubbles that may be trapped in the voids inthe ridged topography of the resist layer RES are displaced and thenumber of gas bubbles reduced. Further, waiting for bubbles to bereleased upon application of immersion liquid LIQ prior to exposing eachtarget area of the substrate can be eliminated or reduced. As a resultof prewetting the resist layer RES with prewetting liquid PLIQ, a fasterand/or better exposure of the resist layer RES may be performed.Furthermore, by prewetting the resist layer RES with prewetting liquidPLIQ, one or more chemicals and/or particles of the resist layer RES mayleach into the prewetting liquid PLIQ for a length of time. In anembodiment, the length of time may be such that a significant amount orsubstantially all of the amount of the one or more chemicals and/orparticles can each have leached into the prewetting liquid PLIQ. Some orall of prewetting liquid PLIQ with the leached chemical(s) and/orparticles may then be removed, for example, by displacement withimmersion liquid LIQ. In this way, liquid through which the patternedbeam is exposed will have a significantly reduced amount of leachedchemical(s) and/or particles, that may detrimentally affect the imagequality.

As illustrated in FIG. 8B, once the prewetting liquid PLIQ is depositedon top of resist layer RES, the substrate W with the resist layer maythen be brought in contact with the immersion liquid LIQ. The prewettingliquid PLIQ and the immersion liquid LIQ may have different chemicalcompositions. However, in an embodiment, the prewetting liquid PLIQ isselected to have substantially the same composition as the immersionliquid LIQ. This is done to ensure that the two liquids LIQ and PLIQ aremore compatible. In an embodiment, the two liquids LIQ and PLIQ aremaintained at a same temperature so as to reduce or eliminate anypossible difference in the refractive index between the two liquids asany variation in the refractive index may reduce the imaging quality. Inthis way, providing immersion liquid LIQ to the resist layer RES thatwas previously prewet with prewetting liquid PLIQ should not have anyproblems that would otherwise arise if the immersion liquid and theprewetting liquid are incompatible.

By prewetting the substrate W with prewetting liquid PLIQ, a surface ofthe resist layer RES is rendered compatible with the immersion liquid.In other words, by prewetting the substrate with prewetting liquid PLIQ,a surface of resist layer is rendered less repellent to the immersionliquid LIQ. For example, the resist layer or a topcoat on the resistlayer may be chemically activated such that the resist layer or topcoatis hydrolyzed and made more hydrophilic.

The immersion liquid is selected to be at least partially transparent tothe radiation beam so that at least a portion of the radiation beamwould reach the resist layer.

In an embodiment, the prewetting liquid PLIQ can be selected to comprisewater and the immersion liquid LIQ can be selected to also comprisewater. In another embodiment, the prewetting liquid is selected tocomprise a topcoat, such as AQUATAR, manufactured by ClariantCorporation.

Prewetting all or part of the resist of the substrate is performed inthe lithographic apparatus prior to exposing a target portion of thesubstrate to radiation. For example, in the embodiment shown in FIGS. 9Aand 9B, the prewetting operation takes place at a station 30 in thelithographic apparatus prior to exposure of the substrate at an exposurestation 32 in the lithographic apparatus. In this particular case, thestation 30 includes a measurement station 30 which is a position of thesubstrate table WT (shown for example in FIG. 1) in the lithographicapparatus at which measurement and/or various alignment operations ofthe substrate table WT and/or the substrate W take place. Measurementsystems are used at the measurement station 30 which include, forexample, measurement sensors 34 (e.g. optical encoders, capacitivesensors, etc.). The exposure station 32 is a position in thelithographic apparatus where the exposure of the substrate W toradiation through the projection lens system takes place. In anembodiment, station 30 may be a prealignment station 30 where thesubstrate is prealigned, typically inside a substrate handling chamberin the lithographic apparatus, prior to being disposed by a substratehandler robot on the substrate table WT, for example. Generally thestation 30 may be almost any location or locations in the lithographicapparatus including the substrate handling chamber, so long as a portionof the substrate can be prewet before supply of the immersion liquid toand exposure of that portion of the substrate, indeed, station 30 may bethe exposure station 30. In an embodiment, the prewetting is performed“off line” at a position so that the time for the substrate to bewetted, bubbles removed, etc. will not hold up the lithographic process.

FIGS. 9A and 9B show an example in which two substrate tables WT aremoved or swapped between station 30 and exposure station 32. FIGS. 9Aand 9B show, respectively, side and top views of the exposure station 32and the station 30. In this case, station 30 includes a measurementstation. The swap of the two substrate tables WT is indicated in FIGS.9A and 9B by a dotted line. In an embodiment, two substrate tables maymove between two stations 30 and an exposure station 32, wherein onesubstrate table moves between one station 30 and the exposure station 32and the other substrate table moves between the other station 30 and theexposure station 32 such that the two substrate tables alternately sharethe exposure station 32. A potential advantage of including such anarrangement in one lithographic apparatus is a possible increase inthroughput, in that one substrate may be exposed while the nextsubstrate to be exposed is being measured. For example, levelingmeasurements may be carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus may have only one table in which case the measurement stationand the exposure station may be at one location or at two locations asthe substrate table moves between the locations.

A liquid supply system 36A, 36B is provided in the lithographicapparatus. The liquid supply structure 36A is configured to supplyprewetting liquid PLIQ on top of resist layer RES at, for example, themeasurement station 30 and the liquid supply structure 36B is configuredto supply immersion liquid LIQ at the exposure station 32 in a spacebetween the prewet substrate W and the projection system PL.

The liquid supply structure 36A comprises an inlet 37 connected to aliquid source 38 which contains the prewetting liquid PLIQ. The inlet 37is adapted to apply liquid PLIQ on top of the resist layer RES. Theliquid supply structure 36A further comprises an outlet 39 connected toa pump 40 so as to remove liquid PLIQ from resist layer RES.

The liquid supply structure 36B comprises an inlet 41 connected to aliquid source 42 which contains the immersion liquid LIQ. The inlet 41is adapted to supply immersion liquid LIQ on top of the resist layerRES. The liquid supply system 36B further comprises an outlet 43connected to a pump 44 to take up the immersion liquid LIQ. As statedabove, the prewetting liquid and the immersion liquid LIQ can be thesame, similar or completely different. In the case where the two liquidsare different, the two liquids are dispensed from two different sources38 and 42. In the case where the two liquids are the same, for exampleboth liquids are water, then a single source of liquid may be used.Suitable piping may be provided to distribute the liquid to desiredlocations in the lithographic apparatus to prewet the substrate W in onelocation of the lithographic apparatus (e.g., the measurement station)and to provide immersion liquid between the projection system PL and theprewet substrate W in another location of the substrate (the exposurestation).

Although the prewetting operation is described above as taking place ata measurement station, the prewetting may take place anywhere in thelithographic apparatus. For example, the prewet operation. can takeplace between the measurement station 30 and the exposure station 32,for example, during the operation of swapping of the two substratetables WT.

In another example, the prewetting may take place at an exposure stationin a localized liquid supply system immersion lithographic apparatus byprewetting specific target portions on the substrate before that targetportion is exposed or by prewetting the substrate completely and thenexposing each target portion thereafter.

Further, in an embodiment, outlet 30 and/or outlet 40 may be used toremove excess prewetting liquid. For example, prewetting liquid may comeinto contact with portions of the substrate or substrate table thatshould not be wet. In another embodiment, there may be too much liquidapplied or liquid applied unevenly. Additionally, or alternatively,outlet 39 and/or outlet 40 may be used to remove most of the prewettingliquid so as to leave only a small portion of liquid filing the crevicesof the resist layer. For example, a thin film of prewetting liquid of,for example, less than 2 μm may be left to fill the crevices of theresist. A thin film of prewetting liquid may be advantageous in helpingreduce evaporative cooling that may otherwise occur if there is too muchof prewetting liquid. Reducing evaporating cooling will help inminimizing ovelay problems. This may be advantageous, for example, toremove prewetting liquid containing leached chemical(s) and/orparticles.

FIG. 10 shows an example diagram of the various steps taking place in alithographic apparatus during transfer of the substrate for prewettingand other procedures according to an embodiment of the presentinvention. The substrate is supplied via supply track 50 to alithographic apparatus 52 with a layer of resist in a dry state (54).The substrate is positioned in a measurement station where variousmeasurements are carried out on the substrate (56). The resist layer ofthe substrate is then prewet with the prewetting liquid (58), optionallyafter the substrate is sent to a prewetting station. After prewettingthe resist layer of the substrate, the substrate is transferred to anexposure station where various alignment procedures are performed toalign the mask or reticle with the substrate (60) and exposure of thesubstrate takes place (62). Although the prewetting of the substrate isshown, in this example, taking place prior to performing the variousalignment procedures to align the mask with the substrate, it is alsopossible to prewet the substrate just before exposure of the substrateafter performing the various alignment procedures. After exposing thesubstrate to radiation, the substrate is sent to a post exposure area sothat the resist layer can be subjected to other procedures, such as apost-bake, development, a hard bake and measurement and/or inspection ofthe imaged features (64). This array of procedures may be used as abasis to pattern an individual layer of a device, for example an ICdevice. Such a patterned layer may then undergo various processes suchas etching, ion-implantation or doping, metallization, oxidation,chemical/mechanical polishing, etc., all intended to finish off anindividual layer. If several layers are required, then it may benecessary to repeat the whole procedure or a variant portion thereof,for each new layer, with overlay (juxtaposition) of the various stackedlayers being performed as accurately as possible. The dashed arrow 66 inFIG. 10 indicates that the substrate may be sent back to thelithographic apparatus for further processing, i.e. for building otherlayers of the device. Eventually, an array of devices may be present onthe substrate. These devices may then be separated from one another by atechnique such as dicing or sawing. The devices may then be mounted on acarrier, connected to pins etc. Further information regarding suchprocesses can be obtained, for example, from the book “MicrochipFabrication: A Practical Guide to Semiconductor Processing,” ThirdEdition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN0-07-067250-4.

While the discussion above has focused mostly on prewetting thesubstrate, it will be appreciated that other structures to whichimmersion liquid is applied for exposure to a patterned beam ofradiation may be prewet. For example, a surface of the substrate tablemay be prewet. A particular example of a portion of the substrate tablethat may be prewet is a surface of a measurement sensor (such as atransmission image sensor or a dose sensor) or a measurement mark (suchas an alignment grating) in or on the substrate table that is configuredto be exposed to a patterned beam of radiation from the patterningdevice or patterned by a grating (e.g., an alignment mark).

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, where applicable, the invention may takethe form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein.

One or more embodiments of the present invention may be applied to anyimmersion lithography apparatus, such as those types mentioned above,and whether the immersion liquid is provided in the form of a bath oronly on a localized surface area of the substrate. A liquid supplysystem is any mechanism that provides a liquid to a space between theprojection system and the substrate and/or substrate table. It maycomprise any combination of one or more structures, one or more liquidinlets, one or more gas inlets, one or more gas outlets, and/or one ormore liquid outlets, the combination providing and confining the liquidto the space. In an embodiment, a surface of the space may be limited toa portion of the substrate and/or substrate table, a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.Furthermore, the immersion liquid used in the apparatus may havedifferent compositions, according to the desired properties and thewavelength of exposure radiation used. For an exposure wavelength of 193nm, ultra pure water or water-based compositions may be used and forthis reason the immersion liquid is sometimes referred to as water andwater-related terms such as hydrophilic, hydrophobic, humidity, etc. maybe used.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A device manufacturing method, comprising: applying, in alithographic apparatus, a prewetting liquid on top of a layer ofradiation sensitive material of a substrate, on a substrate table, or onboth; providing an immersion liquid for use in projecting a patternedbeam of radiation on the prewet substrate and/or substrate table toliquid-to-liquid contact the prewetting liquid; and projecting apatterned beam of radiation, through the immersion liquid, onto thesubstrate and/or the substrate table.
 2. The method according to claim1, wherein the prewetting liquid has substantially a same chemicalcomposition as the immersion liquid.
 3. The method according to claim 1,wherein the prewetting liquid comprises water.
 4. The method accordingto claim 1, wherein the prewetting liquid comprises topcoat.
 5. Themethod according to claim 4, wherein the topcoat includes fluoro alkylacid, homopolymer and water.
 6. The method according to claim 1, whereinthe immersion liquid comprises water.
 7. The method according to claim1, wherein applying the prewetting liquid reduces bubbles of gas trappedbetween ridges in a surface of the radiation sensitive material and/orreduces bubbles of gas trapped between ridges in a surface of thesubstrate table.
 8. The method according to claim 1, wherein applyingthe prewetting liquid fills voids in a surface of the radiationsensitive material with the prewetting liquid and/or fills voids in asurface of the substrate table.
 9. The method according to claim 1,wherein substantially all chemicals, particles, or both of the radiationsensitive material are leached into the prewetting liquid.
 10. Themethod according to claim 1, wherein applying the prewetting liquidrenders a surface of the radiation sensitive material compatible withthe immersion liquid.
 11. The method according to claim 1, whereinapplying the prewetting liquid renders a surface of the radiationsensitive material less repellent to the immersion liquid.
 12. Themethod according to claim 1, wherein the prewetting liquid is at leastpartially transparent to the patterned beam of radiation.
 13. The methodaccording to claim 1, further comprising removing at least a portion ofthe prewetting liquid from the prewet substrate prior to providing theimmersion liquid.
 14. The method according to claim 1, wherein applyingthe prewetting liquid comprises supplying the prewetting liquid with afirst liquid supply system and providing the immersion liquid comprisessupplying the immersion liquid with a second liquid supply system. 15.The method according to claim 1, wherein applying the prewetting liquidcomprises supplying the prewetting liquid at a first location in thelithographic apparatus and providing the immersion liquid comprisessupplying the immersion liquid at a second location, displaced from thefirst location, in the lithographic apparatus.
 16. The method accordingto claim 15, wherein the first location is a location of a measuringstation in the lithographic apparatus and the second location is alocation of an exposure station in the lithographic apparatus.
 17. Adevice manufacturing method, comprising: applying, in a lithographicapparatus, a prewetting liquid on top of a layer of radiation sensitivematerial of a substrate, on a substrate table, or on both; providing animmersion liquid on to the prewetting liquid on the substrate and/orsubstrate table to liquid-to-liquid contact the prewetting liquid whenthe substrate and/or substrate table is under a projection system of thelithographic apparatus for exposure to a patterned beam of radiation;and projecting a patterned beam of radiation, through the immersionliquid, onto the substrate and/or the substrate table.
 18. The methodaccording to claim 17, wherein applying the prewetting liquid comprisessupplying the prewetting liquid with a first liquid supply system andproviding the immersion liquid comprises supplying the immersion liquidwith a second liquid supply system.
 19. The method according to claim17, wherein applying the prewetting liquid comprises supplying theprewetting liquid at a first location in the lithographic apparatus andproviding the immersion liquid comprises supplying the immersion liquidat a second location, displaced from the first location, in thelithographic apparatus.
 20. The method according to claim 17, furthercomprising removing at least a portion of the prewetting liquid from theprewet substrate prior to providing the immersion liquid.
 21. A methodof preparing a substrate provided at least partially with a layer ofradiation sensitive material, prior to applying an immersion liquid tothe substrate and exposing the substrate to a patterned beam ofradiation in an immersion lithographic apparatus, comprising: coating atleast a portion of a surface of the layer of radiation sensitivematerial with a liquid chemical non-sensitive to the patterned beam ofradiation, the liquid chemical remaining in liquid form at least untilapplication of the immersion liquid in the immersion lithographicapparatus to liquid-to-liquid contact the liquid chemical.
 22. Themethod according to claim 21, wherein the liquid chemical is lessrepellent to the immersion liquid applied in the apparatus than theradiation sensitive material is to the immersion liquid.
 23. The methodaccording to claim 21, wherein the liquid chemical has substantially asame chemical composition as the immersion liquid.